In the United States in the 1990s, the incidence of reported pertussis in adults, adolescents and infants increased; infants younger than 1 year of age had the highest reported incidence.
In 4 states with Enhanced Pertussis Surveillance, we examined the epidemiology of reported pertussis cases to determine the source of pertussis among infants. A source was defined as a person with an acute cough illness who had contact with the case-infant 7-20 days before the infant's onset of cough.
The average annual pertussis incidence per 100,000 infants younger than 1 year of age varied by state: 22.9 in Georgia; 42.1 in Illinois; 93.0 in Minnesota; and 35.8 in Massachusetts. Family members of 616 (80%) of 774 reported case-infants were interviewed; a source was identified for 264 (43%) of the 616 case-infants. Among the 264 case-infants, mothers were the source for 84 (32%) and another family member was the source for 113 (43%). Of the 219 source-persons with known age, 38 (17%) were age 0-4 years, 16 (7%) were age 5-9 years, 43 (20%) were age 10-19 years, 45 (21%) were age 20-29 years and 77 (35%) were age ≥30 years.
The variation in reported pertussis incidence in the 4 states might have resulted from differences in awareness of pertussis among health care providers, diagnostic capacity and case classification. Among case-infants with an identifiable source, family members (at any age) were the main source of pertussis. Understanding the source of pertussis transmission to infants may provide new approaches to prevent pertussis in the most vulnerable infants.
From the *Bacterial Vaccine Preventable Diseases Branch, National Immunization Program, Centers for Disease Control and Prevention, Atlanta, GA; the †Minnesota Department of Health, Minneapolis, MN; the ‡Illinois Department of Public Health, Springfield, IL; the §Georgia Division of Public Health, Atlanta, GA; and the ∥Massachussetts Department of Public Health, Jamaica Plain, MA
Accepted for publication September 8, 2004.
Supported by the National Immunization Program, U.S. Centers for Disease Control and Prevention.
Ms. Cianfrini's current affiliation: élan Pharmaceuticals, Inc., 7475 Lusk Boulevard, San Diego, CA 92121.
Reprints not available.